1. Field of the Invention
The present invention relates to improvements in fluid metering rolls or, as they are often referred to, anilox rolls.
Anilox rolls are frequently employed in the printing industry to transfer accurately metered amounts of ink from a fountain roll coated with ink picked up from an ink bath or reservoir or from the bath itself to a printing roll or the like. The anilox roll is typically wiped by a doctor blade or the like to assure even filling of the cells impressed in the surface thereof. Metered quantities of ink from the cells are thence transferred to a printing plate roller or cylinder, which in turn transfers ink patterns to the sheet or web to be printed, the web being passed in the nip between the plate roller or cylinder and an impression cylinder.
2. The Prior Art
Conventional anilox rolls have included a multiplicity of closely spaced cells, the configurational characteristics of which may be varied in accordance with the transfer characteristics of the inks with which they are intended to be used. Generally such cells may be in the form of inverted hemispheres, pyramides, cones or the like, the roll including land areas between adjacent cells which define a wiping or support area for the doctor blade.
Representative examples of anilox rolls having cells of the type hereinabove set forth may be found in U.S. Pat. Nos. 2,217,552 of Oct. 8, 1940; 2,393,529 of Jan. 22, 1946; 3,651,758 of Mar. 28, 1972 and 3,974,554 of Aug. 17, 1976.
Examples of anilox rolls having special cell characteristics may be found in U.S. Pat. No. 3,613,578 of Oct. 19, 1971, assigned to the assignee of the instant application. U.S. Pat. Nos. 4,009,658 of Mar. 1, 1977 and 4,301,730 of Nov. 24, 1981, both likewise owned by the assignee hereof, are examples of anilox rolls having improved wear characteristics by virtue of the formation of the cells in a ceramic coating or matrix.
U.S. Pat. No. 4,155,766 of May 22, 1979 is directed to a half tone screen for rotary gravure printing. U.S. Pat. No. 4,301,583 of Nov. 24, 1981 is directed to an anilox roll. The last two mentioned patents are characterized in that the cells defined in the surface of the roller include connecting channels. This feature is said to facilitate ink distribution, and in the case of U.S. Pat. No. 4,301,583 to minimize moire effects and ink drying or caking in the cells.
There has recently been a trend to the use of high viscosity inks. This trend has, in no small measure, been spurred by the requirements of various governmental authorities that the use of viscosity reducing solvents be minimized.
The use of high viscosity inks has greatly increased the tendency of such inks to clog or cake in the cells, with the result that after relatively short periods the roll is no longer capable of depositing reliably consistent quantities of ink.
A further problem inhering in the use of high viscosity inks with conventional rollers resides in a greater tendency toward the formation of striations in the printed material. These striations are in a measure caused by difficulties in inducing an even spreading of the ink across the width of the roller, a difficulty which is exacerbated by the caking tendency discussed above, especially where the impressions include areas necessitating high ink density and closely adjacent areas where there is to be little or no ink density on the printed image.
A further drawback of known anilox rolls resides in the tendency toward the creation of moire effects, especially unless particular care is taken by the organization creating the printing cylinder to orient the pattern of the cylinders in such manner as to assure a non-registering relation with the pattern of the anilox roll.
While roll configurations such as shown in U.S. Pat No. 4,301,583 have, in a measure, provided somewhat improved results where used in conjunction with high viscosity inks, the results have been less than totally satisfactory in that ink clogging and caking have remained a problem.